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ABSTRACT: Chronostratigraphic Calibration of Late Neogene, Northeast Pacific Planktic Foraminiferal Events: Geological Applications to the Pliocene-Pleistocene of the Ventura Basin, California

Martin B. Lagoe

An integrated chronostratigraphy of late Neogene active margin basins of the northeastern Pacific Ocean is developed by calibrating temperature north Pacific planktic foraminiferal evolutionary datums and paleoclimatically controlled coiling shifts of Neogloboquadrina pachyderma with paleomagnetic, radiometric, and isotopic stratigraphies. This regional chronostratigraphic framework is then adapted to individual sedimentary basins. Ongoing work in the Ventura basin illustrates such an application. Planktic foraminiferal events at Balcom, Wheeler, and Santa Paula canyons are calibrated against paleomagnetic stratigraphy and radiometrically dated ash layers. This calibration agrees with and supplements previously derived regional calibrations. In particular, several coiling shifts of N. pachyderma and the last occurrence datums of Neogloboquadrina asanoi and Noegloboquadrina humerosa appear most useful in this area. These events provide high-resolution chronostratigraphic control between approximately 2.6 and 0.7 Ma in the central Ventura basin. Such chronostratigraphic control is an integral part of geohistory analysis, an application of which is presented to illustrate the utility of the integrated chronostratigraphic framework. Geohistory analysis of the Balcom and Wheeler Canyon sections is used to reconstruct stratigraphic evolution north and south of the Oakridge fault during deposition of the Pico Formation. Both sections show rapid subsidence during the Repettian, slower subsidence or possible uplift during the Venturian, and renewed subsidence duri g the Wheelarian. These histories do differ in several respects and a comparison of subsidence, uplift, and rock accumulation rates indicates that the fault was a normal fault, down to the north, through most of its Pliocene-Pleistocene history, being reactivated as a high-angle reverse fault only during the late Pleistocene.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990